Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations (readOnlyHint=false, idempotentHint=true), it discloses that the call opens a persistent WebSocket session, that repeating it is the recovery path after a restart, and the specific failure signal 'not_logged_in'. It also quantifies payload cost (~20 KB new city, >150 KB late round), which is exactly the kind of behavioral context annotations cannot convey.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the action and its side effect, then failure/recovery, then payload sizing — a sensible priority order with no filler sentences. It is slightly long and re-enumerates snapshot options already present in the schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For an auth tool with an output schema, it covers credentials, session side effects, recovery conditions, and response-size tradeoffs. An agent has everything needed to call it correctly and to recover when it is called at the wrong time.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline is 3, but the description adds decision-relevant meaning: it explains the default is full, summarizes what snapshot='city' returns, notes that 'now is always included' with sections, and gives a size-based rationale for choosing the cheaper options. It largely restates the schema enum values rather than extending them, so not a 5.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Log into an existing Agentic Kingdoms account by email/password'), plus the side effect of opening the game connection. The word 'existing' distinguishes it from register, guest_login, and claim_account among the siblings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit trigger for re-invocation ('after the MCP server restarted', a tool answering not_logged_in, or an expired MCP session), which is real when-to-use guidance. It does not explicitly name register/guest_login as the alternatives for callers who lack an account, leaving that routing to inference from 'existing account'.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.